1. Field of Invention
The present invention relates to a pneumatic tire, more particularly to a carcass and tread band structure in which specific polyethylene-2,6-naphthalate fiber cords are used to improve tire performance such as steering stability, ride comfort, rolling resistance, road noise and durability.
2. Description of Related Art
In the radial tires for high-speed use such as passenger car tires for example, a tread band is usually provided on the radially outside of the breaker to improve high-speed durability of the tire.
As a result of inventors' study, it was found that road noise (running noise heard inside the car) around 250 Hz can be reduced by using high modulus cords in the tread band. But, it is also found that the road noise can not be effectively reduced if the band cord modulus is simply increased because the stretch of the band during tire vulcanization becomes insufficient as the modulus increases and as a result the vulcanized tire is slightly deformed. Although such deformation is small, vibration is caused during high-speed running and thereby the running noise is deteriorated.
On the other hand, use of high-modulus cords in the carcass become popular in order to reduce the tire weight to improve fuel consumption and improve steering stability and the like. In this case, however, as the sidewall rigidity increases, the ride comfort is liable to deteriorate. Further, there is a possibility of deteriorating the rolling resistance of the tire depending on the cord material.
It is therefore, an object of the present invention to provide a pneumatic tire, in which, the above-mentioned problems can be solved and tire performance such as steering stability, ride comfort, rolling resistance, road noise and durability can be improved in a well-balanced manner by using a polyethylene-2,6-naphthalate fiber cord in the carcass and/or band.